Nancy Lauth-de Viguerie

Thermoresponsive Properties of PNIPAM-Based Hydrogels: Effect of Molecular Architecture and Embedded Gold Nanoparticles

Thermoresponsive hydrogels were successfully prepared from poly(N-isopropylacrylamide)-based polymers with different architectures (linear, branched, or hyperbranched). The macromolecular architectures strongly influence the internal structure of the hydrogels, therefore modulating their thermoresponsive and rheological properties. These hydrogels were used for the in situ synthesis of gold nanoparticles. Significant changes in hydrogel microstructures and in average pore size due to the presence of gold nanoparticles were observed. Additionally, their presence significantly increases both the mechanical strength and the toughness of the hydrogel networks.

Vesicles in ionic liquids.

The formation of vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in several room-temperature ionic liquids, namely, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF(4)), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf(2)), and N-benzylpyridinium bis(trifluoromethylsulfonyl)imide (BnPyNTf(2)), as well as in a water/BmimBF(4) mixture, was investigated. In pure ionic liquids, observations by staining transmission electron microscopy demonstrated clearly the formation of spherical structures with diameters of 200-400 nm. The morphological characteristics of these vesicles in ionic liquids, in particular, the membrane thicknesses, were first investigated by small-angle neutron scattering measurements. The mean bilayer thickness was found to be ∼63 ± 1 Å in a deuterated ionic liquid (BnPyNTf(2)-d). This value was similar to that observed in water. The effect of ILs on the modification of the phase physical properties of multilamellar vesicles (MLVs) was then investigated by differential scanning calorimetry. In pure IL as in water, DPPC exhibited an endothermic pretransition followed by the main transition. These transition temperatures and the associated enthalpies in ILs were higher than those in water because of a reduction of the electrostatic repulsion between zwitterionic head groups. To better understand the effect of ionic liquid on the formation of multilamellar vesicles, mixtures of BmimBF(4) and water, which are miscible in all proportions, were analyzed (BmimBF(4)/water ratio from 0% to 100%). SANS and DSC experiments demonstrated that the bilayer structure and stability were strongly modified by the IL content. Moreover, matching SANS experiments showed that BmimBF(4) molecules prefer to be located inside the DPPC membrane rather than in water.

Mesomorphic ionic hyperbranched polymers: effect of structural parameters on liquid-crystalline properties and on the formation of gold nanohybrids

Branched thermotropic liquid crystals were successfully obtained from ionic interactions between hyperbranched polyamidoamine and sodium dodecylsulfate. These complexes present columnar rectangular and lamellar thermotropic mesophases as demonstrated by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. The relationships between the structural characteristics of the polymers (size of the hyperbranched core, hyperbranched or dendritic nature of the core, and substitution ratio) and the mesomorphic properties were studied. In situ formation of gold nanoparticles was then performed. The templating effect of the liquid crystal mesophase resulted in the formation of isotropic nanoparticles, the size of which was dictated by the local organization of the mesophase and by the molar mass of the hyperbranched complex.

The effect of polymer branching and average molar mass on the formation, stabilization and thermoresponsive properties of gold nanohybrids stabilized by poly(N-isopropylacrylamides)

Branched structures are of crucial importance in the formation of hybrid materials with tunable properties. Nevertheless, little is known about the optimal macromolecular parameters (molecular weight, extent of branching etc.) allowing either control of the growth mechanism of the inorganic core or access to nanohybrids with high colloidal stability. In this paper, the synthesis and characterization of a new family of dendritic polymers comprising a branched polyamidoamine core and a poly(N-isopropylacrylamide) shell are described. In aqueous solutions, a strong dependence of their thermoresponsiveness upon the macromolecular architecture was evidenced by neutron and light scattering techniques and electronic microscopy. These polymers were then employed as stabilizers of gold nanoparticle (AuNP) dispersions by either a posteriori adsorption on NPs or in situ NP formation. Both approaches were successful for stabilization and reversibility of the thermostimulable precipitation process. First, we demonstrated that macromolecular architecture greatly influences the growth mechanism of the in situ formed NPs and their colloidal stability. Whereas small linear polymers allow a better control of NP growth, the branched structures proved to be better stabilizing agents. In contrast, adsorption on preformed AuNPs of controlled size evidenced the higher efficiency of small branched structures than linear or hyperbranched polymers as good stabilizing agents.

Palladate Salts from Chiral Pyridinium Ionic Liquids: Synthesis and Crystal Structures

This paper reports the preparation, characterization and the crystal X-ray structures of metal-containing ionic liquid complexes based on chiral pyridinium cations and tetrachloropalladate (II) [PdCl4]2-.

Surfactant Aggregates in Ionic Liquids and Reactivity in Media

In this paper the association of different families of amphiphilic compounds in room temperature ionic liquids in micelles, vesicles and reverse microemulsions was demonstrated. First the formation of nonionic polyoxyethylene-type surfactant micelles in the ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate is clearly evidenced using tensiometry and dynamic light scattering measurements. Critical micellar concentrations, object sizes and aggregation numbers are given and compared to aqueous and formamide systems. Then, vesicular aggregation of glycerophospholipid DPPC in two ionic liquids bmimBF4 and emimNTf2 was evidenced. Lastly, the phase diagram and microstructure of the ternary system ionic liquid (benzylpyridinium bis(trifluoromethanesulfonyl) imide)/nonionic surfactant (octylphenol ethoxylate)/toluene were studied. Phase stability and small-angle neutron scattering data show the formation of ionic liquid-in-oil microemulsion droplets. These reverse microemulsions were used as nanoreactors to perform a Matsuda-Heck reaction. The reaction yields obtained were greater in microemulsions (67%) than in bulk IL (33%) highlighting a strong effect of confinement. The reactivity in these confined media led to promising results.